Roman Vs Persian hydraulic engineering
While Roman aqueducts have become relics of the past, the Persian Qanats are still in use. Both were engineering marvels requiring very high level expertise in geology, morphology, hydrology, moisture and the ability to compute complex mathematics. But what sets the qanats apart is their functionality and utility, reason why they have survived for centuries and are still in use!
An aqueduct is a channel or pipe-line to transport water over a greater distance from a water source to its destination: often a city, sometimes a farm, or a mill; there the water is distributed. The water is conveyed in the channel or pipe-line based on gravity. The Roman empire had almost a time span of 800 years: from 300 BCE to 400 CE, and was quite extensive: from England to Syria and from Hungary to Libya. So was the distribution of their aqueducts.
Total known aqueducts 1,000–1,500! When the aqueduct shows up near the city a water distribution system was built by means of primary and secondary castella (distribution basins); the water was brought mainly to public street side fountains and bathhouses, sometimes also to selected private individuals (the local elite), mainly connected by lead pipes. Some bigger farmers in the countryside had their own aqueducts for irrigation or tapped (legally & sometimes illegally) a main aqueduct nearby!
The result is that up to 80% of an Roman aqueduct was subsurface and the remaining 20% are bridges, arcades etc. Some of these are still visible in the landscape, like bridges (PdG), arcades (Rome), tunnels (Cave de Curé, France). An aqueduct belonged to the local government or the town council; the construction of the aqueduct was often paid by a maecenas (wealthy patron). Construction was done by contractors with sometimes support from the Emperor and/or the Army by skilled slaves and non-skilled prisoners.
Main characteristics: close to the surface, pipes (often of Greek origin), channels (0.60 x 1.2 m), works of art, public ownership, for public use (fountains and bath houses).
Qanat is an underground water channel consisting of a series of vertical shafts connected at their bottom with a sub-horizontal tunnel (refer illustration). Its function is to exploit a certain aquifer (a water bearing subterranean layer). A qanat pierces an aquifer by means of a well (called the mother well) and a channel, then conveys the water to villages and towns in water scarce area’s at distances of 2–80 kms. The first qanats were constructed in the Iranian plateau probably 800 BCE with mining operations in NW Iran. The Qanat has spread subsequently to other areas, in China, Levant, Meghrab,and Mediterranean areas.
Qanats may reach a depth of 100 m at the ‘mother well’ and a spacing of the shafts of 50–100 m apart. The actual channel is about 0.80 m wide and 1.2–1.5 m high, in which water is flowing free or in a small depression, from the ‘mother well’ to its destination. The qanats represent often the main or only water source for a large population in remote villages but also for oasis cities and major towns. In Iran about 22,000 qanats were operational with a total length of 250,000 kms. Some 40 years ago Tehran was almost completely dependent of a series of qanats for its drinking water supply, till the advent of motorized deep pumps and the construction of dams.
The main use of qanats were/are for drinking water and irrigation. There are elaborate systems on the division the water in time and volume — using sluices, general and local laws, supervisors, etc., The ownership of rural qanats is a quite complex: in many cases a group of families of farmers owns the qanat and so the water — in general qanats have 10–250 owners and formed regulations on how to manage the qanat.
Ab-anbar or water storage tank: water source of a qanat gave a constant output but under certain circumstances storage of water was necessary in huge subterranean basins, often cooled by an ingenious system, and at the same time a place to draw water.
Wind towers or Badgir: part of the scenery of many Iranian towns like Kaskan, Isfahan en Yazd. These towers have a special function in cooling the air, in the basements of buildings (the summer living rooms), patio’s and courtyards.
Yakh-chal or Ice-house: people were storing ice underground in yakhchals. They would collect ice from mountain tops and put them in an underground pit insulated by a special mortar.